1. Field
The present specification generally relates to filters for diesel engine exhaust and, more specifically, to ceramic honeycomb filters for reducing NOx and particulate matter in the exhaust streams of diesel engines and methods for making the same.
2. Technical Background
With the implementation of the EPA 2007 regulations governing diesel exhaust emission in the U.S. the use of diesel particulate filters has been a necessary component of diesel engine exhaust after-treatment systems. The introduction of the EPA 2010 regulations governing diesel exhaust emissions have further regulated nitrous oxide (NOx) emission limits thereby creating a need for alternative solutions for both the reduction of particulate matter and NOx compounds in diesel exhaust.
Another trend of exhaust gas treatment systems is the reduction of the total system volume. Attempts have been made to integrate DeNOx functional catalyst materials into a diesel particulate filter thereby eliminating the need for separate devices. However, there exists a competition for NO2 in the exhaust gas stream between the DeNOx reaction and the soot passive regeneration reaction required to reduce soot loads in the filter. This competition significantly reduces passive regeneration performance of the particulate filter.
Accordingly, a need exists for alternative particulate filters with DeNOx functionality and improved passive regeneration performance.